PENNSYLVANIA — Although spring is typically well underway by May, historical weather records show that measurable snowfall in Pennsylvania, while rare, has occurred.
Data from the National Weather Service and regional climate archives indicate that both trace and measurable snowfall have been documented across Pennsylvania during the month of May. These events are uncommon due to rising average temperatures, but they remain possible under certain weather patterns.
Late-season snowfall requires an unusual combination of factors, including a surge of cold air and a source of moisture.
This can occur when a strong low-pressure system moves through the region while drawing colder air southward from Canada. If atmospheric temperatures—from the surface through higher elevations—are sufficiently low, precipitation can fall as snow instead of rain.
Pennsylvania’s geography plays a role in increasing the likelihood of such rare events. Higher elevations, including areas within the Allegheny Mountains and the Pocono Mountains, are more prone to late-season cold air, making measurable May snowfall slightly more likely there than in lower-lying regions.
Historical records show that parts of Pennsylvania have experienced measurable snowfall into early May, with trace amounts occasionally reported even later in the month. For example, measurable snow was recorded in portions of the state during early May cold snaps in the early 20th century, when widespread unseasonably cold conditions affected much of the Northeast.
Climatologically, the last average snowfall in Pennsylvania typically occurs in April. However, variability in large-scale weather patterns—particularly shifts in the jet stream—can allow cold air to dip farther south than usual, creating conditions favorable for snow even late in the spring.
While the probability remains low, the historical record confirms that measurable snowfall in May has occurred in Pennsylvania. As a result, despite generally mild spring conditions, the possibility of a brief return to winter-like weather cannot be entirely ruled out based on past data.
